Boiler Types were introduced around 1900. The columns below show two early Ivatt types, later Gresley GNR Diagram number (where known), LNER Diagram number (where appropriate). This list is sorted in order of Column 2. The information in the first two columns is based on notes made by Roy Burton, senior draughtsman in Doncaster Locomotive Drawing Office until 1959.
| Early Ivatt type | Later Ivatt type | Gresley Dgm. | LNER Dgm. | Ivatt Engine Classes |
|---|---|---|---|---|
| A3 | A1 | A1 | ||
| A1 | A2 | A2 | ||
| A2 | A3 | A3 | ||
| B1 | B1 | B1 | ||
| B2 | B2 | B2 | ||
| B3 | B3 | B3, B4 | ||
| B4 | B4 | A4, A5 | ||
| C5 | C5 | B6 | ||
| D1 | D1 | 4 | 11 | B7, C2, D2, E1, E4, F3, G4, J5, J8, J16 |
| C6 | D3 | B5, E2, E3 | ||
| D3 | D4 | F2 | ||
| D4 | D6 | J6 | ||
| D5 | D7 | J7 | ||
| D6 | D8 | 4a | G3 | |
| D8 | D9 | 4a | J17 | |
| D9 | D10 | J9 | ||
| D10 | D11 | J10 | ||
| E1 | E1 | 6 | 7 | D1 |
| F1 | F1 | 2 | 4 | C1, K1 |
| F2 | F2 | 2 | 4 | C1 No. 271 |
| J1 | H1 | F1 | ||
| L1 | J1 | F6 | ||
| K1 | J2 | F4 | ||
| O1 | J3 | G2 | ||
| M1 | K1 | F5 | ||
| P1 | K2 | J1, J2, J3 | ||
| N1 | L1 | F7,G5 | ||
| Q1 | M1 | J4 | ||
| R1 | N1 | J11, J12 * | ||
| S1 | O1 | 10 | 9 | J13 |
| T1 | P1 | J14 | ||
| U1 | Q1 | J15 | ||
| V1 | Q2 | J18 | ||
| W1 | R1 | J19, J20 | ||
| X1 | S1 | H1 |
* “GREAT NORTHERN LOCOMOTIVE HISTORY“ (Norman Groves) notes that in the January 1902 Boiler Classifications, Classes J11 and J12 were in Boiler S1. There were thus more changes in the classification than suggested in the table above.